Process for drying laundered garments of polyester fibers



P. E. EBERT Feb. 21, 1967 PROCESS FOR DRYING LAUNDERED GARMENTS OF'POLYESTER FIBERS 2 Sheets-Sheet l Filed Oct. 10, 1963 INVENTOR PHILIPEDMUND EBERT ATTORNEY Feb. 21, P. E. EBERT PROCESS FOR DRYING LAUNDEREDGARMENTS OF POLYESTER FIBERS Filed Oct. 10, 1963 2 Sheets-Sheet 2 FlG-Z/7 TUNNEL DRYER PERFORATED V.

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PLATE DIRECTION OF AIR FLOVI INVENTORv PHILIP EDMUND EBERT BY WZWATTORNEY United States Patent O 3,304,620 PRUCESS FOR DRYING LAUNDEREDGARMENTS GF POLYESTER FIBERS lPhilip Edmund Ehert, Wilmington, Del.,assignor to E. I.

du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware Filed Oct. 10, 1963, Ser. No. 315,234 3Claims. (Cl. 34-31) This invention relates to a process for dryinggarments and, more particularly, to a process for the drying of garmentscontaining polyester fibers.

Commercial laundering of garments conventionally requires three majorsteps, 1) washing, (2) drying, .and (3) finishing. Each of these threemajor steps greatly increases labor costs due to the multiple handling.Finishing, in particular, requires much handling of individual garmentsand, is therefore the highest cost step in the process. Previousattempts to eliminate the finishing step, such as drip-dry, tumble-dry,or hot air-dry have not been entirely successful since at least someironing or pressing usually is required to give the garment a neatappearance. This is particularly true of garments washed at about 70 to80 C., as is the practice in commercial laundries. Even a minimum ofironing or pressing is undesirable since it is still necessary for thegarment to be handled, thus maintaining a high labor cost.

It is an objective of this invention to provide an improved process fordrying garments containing synthetic, linear, polyester fibers in orderto obtain a dry, Wearable garment.

According to this invention there is provided a process for dryinggarments containing at least 65% polyethylene terephthalate fiberscomprising hanging the garments, while dripping Wet, onto racks andpassing them through a dryer wherein the garments are subjected tolmoist air at a temperature of l45 to 155 C. dry-bulb and 85 to 90 C.wet-bulb to produce a dry, essentially wrinklefree garment.

In the drawings, which illustrate the invention,

FIGURE l is a fio'w diagram illustrating the process of this invention.

FIGURE 2 is a schematic cross-sectional view of the drying tunnel usedto dry garments in accordance with the process of this invention.

As shown in FIGURE l, garments to be dried are taken from the washer 3and hung on racks suspended from an endless conveyor track 4. Thegarments are conveyed through a drip area 6 to become free of excesswater, and continue on through a tunnel dryer 7 |where they are dried indrying Chamber 8. The dry garments are then removed from the conveyor atunload area 9.

Referring to FIGURE 2, moist hot air is circulated in a clockwisedirection in tunnel dryer 7 by fan 10, as indicated by the arrows.Saturated steam is introduced into the circulating air at vent 11located adjacent to -opening 12 into fan Chamber 13. The moist air isheated by steam coil 14 in the fan chamber. The dry-bulb temperature ofthe air is measured at dry-bulb therrnometer 15 and the wet-bulbtemperature measured at wet-bulb thermometer 16. The hot, moist air fromchamber 13 enters the drying Chamber 8 through a perforated bottom plate17 and eXits through a perforated top plate 18 after passing around andthrough garment 20 suspended from endless conveyor track 4. The airvelocity is such asto agitate the garment and to insure complete drying.When the air is maintained at the critical driy-bulb and Wet-bulbtemperatures specified previously, the garment is dried in anessentially wrinkle-free condition.

In drying garments in accordance with this invention, it is essentialthat moist heat be used. The moisture content and the temperature |ofthe air are critical if the gar- 3,304,0Z0 Patented Feb. 21, 1967 ICCment is to leave the dryer in a Wrinkle-free condition. This process,while usable in a batch operation, provides the most beneficial resultswhen incorporated into a continuous process.

During the manufacture of polyethylene terephthalate garments the fabricis heat-set in the desired wrinkle-free configuration. This imparts anability to resist wrinkling at normal temperatures. However, washing atelevated temperatures, such as 70 to C. for commercial laundries, setswrinkles in the garments which are not removed during drying inconventional ways. As a result of extensive experiments, it has beenfound that the fabric will resume its original heat-set configuration ifdried under critically controlled conditions with hot, moist air attemperatures sufficiently below that of heat setting and sufi'icientlyabove those at which the wrinkles became set. In evaluating suchexperiments a wrinkle rating is assigned to garments based on thefollowing subjective rating scale:

(l) Extreme wrinkling;

(2) Considerabl-e Wrinkling;

(3) Moderate wrinkling;

(4) Slight Wrinkling;

(5) No wrinkling.

Garments having a wrinkle-rating greater than 4 are essentiallywrinkle-free. In accordance with this invention, as illustrated in thesubsequent example, drying in a current of air having a temperature ofl45 to 155 C. (dry-bulb) and having a moisure content corresponding to aWet-bulb temperature of to C. provides such garments, having theappearance of being ironed or pressed.

Garments having a wrinkle rating of 3 to 4 are Wearable because thewrinkles are inconspicuous 'under normal wearing conditions. Wearablegarments are provided, after washing at about 77 C., by drying in air ata drybulb temperature of at least C. and a Wet-bulb temperature of atleast 77 C. Garments dried at lower dry-bulb or wet-bulb temperatureswould not be regarded as Wearable without ironing or pressing. Airtemperatures higher than about C. (dry-bulb) are not practicallyattainable in commercial operation and .may approach too closely to theoriginal heat-setting temperature. Drying may be undesirably slow atwet-'bulb temperatures above 90 C.

Garments made from fabrics containing a high percentage of syntheticfibers, e.g., 50% or more of nylon or polyester fibers, can be used inpracticing this invention. Preferably, the garment Will be made from afabric consisting of polyethylene terephthalate fibers or a blend ofpolyethylene terephthalate fibers with other natural or synthetic fibersin which at least 65% of the fibers are polyethylene terephthalatefibers. Polyethylene terephthalate fibers are preferred because theyadsorb relatively small amounts'of Water, and because of theireaseof-care properties.

In addition to the critical conditions of the drying medium, wrinkleremoval is favored by heavier fabrics, looser construction, and highpolyester content. Further, directing the air flow upward assists in thedrying process. Upward air flow tends to eliminate moistureconcentration along the bottom edge of vthe garment, allows the air toflow through garments such as dresses and coats, and also agitates thegarment.

The over-all appearance of the garment is further improved if the seamsare pressed prior to the first laundering, since this tends to minimizeseam pucker which detracts from the over-all appearance of the garmenteven though it be wrinkle-free.

In addition to garments, flat goods such as sheets and pillow cases canalso be dried substantially wrinkle-free in accordance With thisinvention.

3 Example l Shirts made from an oxford fabric containing 65%polyethylene terephthalate and 35% cotton fibers are washed at 77 C. Thehighly wrinkled garments are placed, dripping wet, on hangers and hungfour inches apart on a moving, endless conveyor track leading to atunnel-type dryer. On the way to the dryer, the garments are allowed todrip for approximately minutes to remove excess water. The shirts thenpass into a drying tunnel. Runs A through I are made with the conditionsfor each run shown iu Table I. In each of the runs the air is directedupward at 'approximately 175 feet per minute to agitate the shirts. Theshirts have a residience time in the dryer of minutes and exit from 'thedrying tunnel, completely dry, at the rate of about 300 per hour. Thedry garments are removed from the conveying track and theirwrinkle-rating determined by visual inspection. The averagewrinkle-rating of the skirts of each run is recorded in Table I.Moisture is introduced into the drying tunnel by opening a valve locatedin a two-inch line carrying saturated steam at a pressure of 120p.s.i.g. For a given dry-bulb temperature, the wet-bulb temperature iscontrolled by the amount of steam introduced to the drying tunnel, thewet-bulb readings increasing with increasing moisture content. In runs Dand J, no moisture was added to the air.

From Table I it can be seen that a high wrinkle rating is obtained atonly the highest dry-bulb temperature and highest moisture content,i.e., as shown -by run A. Good,

though less desirable, results are obtained at either the same hightemperature and a lower moisture content (run B), or at a lower dry-bulbtemperature and the high moisture content (run E). Run J isrepresentative of maximum conventional drying conditions, and theseconditions result in highly wrinkled shirts exiting from the dryingtunnel. Increasing the dry-bulb temperature without increasing thewet-bulb temperature, as in run D, somewhat improves the appearance ofthe shirts but they still contain excessive wrinkles.

Since many different embodiments of the invention may be made Withoutdeparting from the spirit and scope thereof, it is to be understood thatthe invention is not limited by the specific illustrations except to theextent defined in the following claims.

I claim:

1. In the process of drying laundered garments in a tunnel-type dryer,the improvement for producing dry, essentially wrinkle-free garmentsfrom dripping wet garments contaning at least polyethylene terephthalatefibers, which comprises hanging said wet garments on racks, continuouslyconveying the garments through the dryer, blowing moist air at adry-bulb temperature of 145 to 155 C. and and a web-bulb temperature ofto C. through the garments within the dryer until said wet garments dryin an essentially wrinkle-free condition, and then removing the drygarments from the conveyor.

2. A process as defined in claim 1 wherein said moist air is blownupward through the garments at sufficient Velocity to agitate thegarments.

3. A process as defined in claim 2 wherein said moist air has a dry-bulbtemperature of 149 C. and a wet-bulb temperature of 88 C.

References Cited by the Examiner UNITED STATES PATENTS 2,654,162 10/1953Long et al. 34-46 X 2,698,488 1/1955 Cannon et al. 34-46 X 3,102,7969/1963 Erickson 34-216 X FREDERICK L. MATTESON, JR., Primary Examner. D.A. TAMBURR-O, Assistant Examiner.

1. IN THE PROCESS OF DRYING LAUNDERED GARMENTS IN A TUNNEL-TYPE DRYER,THE IMPROVEMENT FOR PRODUCING DRY, ESSENTIALLY WRINKLE-FREE GARMENTSFROM DRIPPING WET GARMENTS CONTAINING AT LEAST 65% POLYETHYLENETEREPHTHALATE FIBERS, WHICH COMPRISES HANGING SAID WET GARMENTS ONRACKS, CONTINUOUSLY CONVEYING THE GARMENTS THROUGH THE DRYER, BLOWINGMOIST AIR AT A DRY-BULB TEMPERATURE OF 145* TO 155*C. AND AND A WEB-BULBTEMPERATURE OF 85* TO 90*C. THROUGH THE GARMENTS WITHIN THE DRYER UNTILSAID WET GARMENTS DRY IN AN ESSENTIALLY WRINKLE-FREE CONDITION, AND THENREMOVING THE DRY GARMENTS FROM THE CONVEYOR.